The communications industry has developed and manufactured a number of communications devices and methods aimed at satisfying a large and ever-growing demand for communicating data. For industrial applications, a central data collection site may have a need for acquiring information from a variety of remotely located monitoring devices that collect data about the operation or performance of industrial equipment. Operators of a central control site also may have a need to cause a remotely located device to perform some operation. The communications systems and methods developed in this area by the communications industry are collectively referred to as telemetry.
Generally, telemetry is the technology of automatic data measurement and transmission, as by wire or radio, from remote devices, to a central station for recording and analysis. Telemetry can also involve communications in the opposite direction, i.e., from the central station to the remote devices. Data communication in both directions may be utilized to provide a closed loop control system. For example, the operator of an oil pipeline may control flow within the pipeline by controlling the opening of a valve in the pipeline. For the purposes of this discussion, data communication from the central station to the remote device is termed "forward communication"; data communication from the remote device to the central station is termed "reverse communication". In the oil pipeline example, a reverse communication could provide to the operator data on the flow of oil through the pipeline. A forward communication could transmit a signal from the operator to a valve to reduce the flow of oil, thereby completing the closed loop control system.
Wireless communications have been extensively used to support telemetry systems. A common form of wireless communication for both voice and data transmissions is the cellular mobile radiotelephone (CMR) system, which is connected to the extensive public switched telephone network (PSTN) and permits communications between a mobile radiotelephone user and anyone with a conventional telephone (or another radiotelephone). Typical CMR systems are characterized by dividing a radio coverage area into smaller coverage areas or "cells" using low power transmitters and coverage-restricted receivers. CMR systems typically include control channels for establishing communication between the CMR system and a radiotelephone and voice channels for providing real-time communications between a radiotelephone and another party. As shown in U.S. Pat. Nos. 3,906,166 and 4,268,722, the limited coverage area enables the radio channels used in one cell to be reused in another cell. As a cellular mobile radiotelephone within one cell moves across the boundary of the cell and into an adjacent cell, control circuitry associated with the cells detects that the signal strength of the radiotelephone in the just-entered cell is stronger, and communications with the radiotelephone are "handed-off" to the just-entered cell. Thus, a CMR system can supply two-way communications for an array of cells, thereby supplying communications for a much wider area than conventional two-way wireless communication systems.
Many of the telemetry systems that have been made available by the communications industry utilize existing CMR systems. The benefit of these telemetry systems is that they are operable within the architecture of the existing CMR systems and, therefore, are readily and inexpensively implemented. Unfortunately, many such telemetry systems utilize the voice channels of the radiotelephone system to transmit data-only communications. Conventional radiotelephones generally offer both voice and data communications capabilities and, accordingly, the radiotelephone service is generally supplied at a cost that is commensurate with the combined voice and data services. Nevertheless, this combination of both voice and data communications may exceed a user's requirement for communicating by only data. In addition, real-time voice or data communications is not always desirable by a user who wishes only to receive a message without having a current activity disturbed. As with other wireless communication systems, the frequency spectrum for the CMR system radio channels, particularly voice channels, is a limited resource.
U.S. Pat. No. 5,546,444, assigned to the assignee for the present application, describes a system for obtaining data and communicating data (rather than voices) over the control channels of a CMR system. Utilizing the control channels to communicate data conserves the valuable frequency spectrum allocated for the voice channels that support normal telephone conversations on the CMR system. Because the system can be implemented within the confines of the conventional CMR system, no significant modification is required to accommodate the ability to communicate data over the control channels.
An illustration of the use of a control channel to communicate data is provided by the oil pipeline example discussed above. By connecting a modified radiotelephone transceiver to a flow meter, data generated by the flow meter can be collected by a monitoring device and communicated by the transceiver, via the control channel, to a central data collection system. An interface between the monitor and the transceiver can convert the data to a format that is communicable by the transceiver. This combination of a transceiver, monitor, and interface operates as a data reporting device. The central data collection system can transmit a message (i.e., control message) via a forward control channel (FOCC), to the data reporting device in order to trigger a communication of the collected data. The data reporting device can respond by transmitting a message via a reverse control channel (RECC), to the central data collection system. Instead of sending the information normally used for registering the device's identity or originating a call request, however, the data reporting device can replace such information with the collected data for transmission via the control channel. Without establishing a voice channel connection, the collected data is, nonetheless, communicated to the central data collection system.
Reverse communications (via the RECC) of selected data, by a data reporting device, are referred to as data messages. Forward communications (via the FOCC) are referred to as control messages. Control messages contain a mobile identification number (MIN) which identifies the cellular device to which the control message is directed. Typically, only cellular devices with a matching MIN stored in memory will respond to the control message. The most common type of control message is the page message, which notifies the cellular device of an incoming call. Other control messages instruct the cellular device to perform other communication functions, such as to display a message waiting indicator or to generate an autonomous registration.
A data reporting device can be programmed to respond to a control message, received from the data collection system, by performing operations other than simply sending a data message to the data collection system. By equipping the data reporting device with a control unit, rather than (or in addition to) a monitor, the data reporting device can be utilized to provide a means of remote control. Returning to the oil pipeline example, the data collection system may transmit a control message to the data reporting device to close the oil pipeline valve. In this simple case, the data reporting device is programmed to trigger the valve closing when the device receives the control message from the data collection system. A second data reporting device could be used to open the valve when the second data reporting device receives a control message. Thus, by "calling" the first data reporting device, the data collection system closes the valve and, by "calling" the second data reporting device, the data collection system opens the valve.
Depending on the amount of data that can be communicated over the control channel from the data collection system toward the data reporting device, the data reporting device can be programmed to perform a number of operations. For example, if the remote device is only capable of receiving a control message and no accompanying data, then the remote device can only respond with a single operation. If, on the other hand, accompanying data can be sent with the control message, then the accompanying data can define which operation from a list of available operations that the remote device should perform. Instead of having two data reporting devices as described above, the oil pipeline valve could be operated with only one data reporting device. When a control message is placed by the data collection system to this data reporting device, the data collection system could also transmit an operation identifier as accompanying data to indicate that the valve should open or close.
Current CMR system-based data message systems are unable to provide the forward direction data capacity necessary to trigger more than one responsive operation. Specifically, current systems are designed to transmit a control message to a data reporting device and the data reporting device is designed to be responsive to that control message with a single operation. In order to perform more than one operation at a single remote site, current systems require either more than one data reporting device to be located at the site or the utilization of data reporting device that is responsive to more than one MIN. Either method is limited in the number of operations that can be requested, therefore, there is a need to define more operations within the transmitted control messages. Data reporting devices are expensive and there is a need to minimize the number of data reporting devices that are required to perform a number of operations at a single remote site.
Accordingly, there is a need to overcome the limitations of the prior art by adapting an existing telecommunications network to communicate data and/or operation identifiers from a central control system to a data reporting device, thereby enabling a single data reporting device to perform a number of operations with a single control message. There is also a need to expand the data capacity of the existing telecommunications network, such that an operation identifier communicated from the central control system to the remote data reporting device can identify any one of a number of available operations for the remote data reporting device to perform. This new use of an existing communications system should have a minimum impact upon present communications carried by the system. The present invention adapts the existing architecture of a CMR system in an efficient and cost-effective manner to support data communications via the CMR system, including the collection and reporting of data recorded at remote sites as well as the multi-operation functionality of the remote devices at the remote sites.